In a 1982 paper in the journal Glossa, Pullum outlined a set of arguments for treating English infinitival to as a defective auxiliary verb. Twenty years later, in his entry on infinitival constructions in The Cambridge Grammar of the English Language (CGEL, 2002), Huddleston argues that several distributional facts about auxiliaries fit poorly with this hypothesis. He proposes, on the basis of significant structural parallels, that to is a subordinator (complementizer). I show that Huddleston's arguments constitute a flawed analysis in CGEL's otherwise superb coverage of English descriptive grammar, and that the facts run strongly counter to his claims, often falling out independently from generalizations about auxiliaries that Huddleston overlooks. Several of these points were anticipated in Pullum's paper, but recent research on an idiosyncratic auxiliary-specific pattern of English nonrestrictive relative clause formation provides a powerful new argument in support of the auxiliary claim. In this respect, as in all others, the assignment of to to the class of auxiliaries provides the simplest and broadest account of its syntactic behavior.